In the past, as an exhaust gas purification catalyst arranged in an exhaust passage of an internal combustion engine, there has been developed an electrically heated catalyst (hereinafter, may also be referred to as an EHC) in which a catalyst is heated by means of a heat generation element which generates heat by electrical energization thereof.
In the EHC, the heat generation element is provided with a pair of electrodes for supplying electricity thereto. Each of the electrodes has a surface electrode which spreads along the surface of the heat generation element. The surface electrodes are arranged in opposition to each other with the heat generation element being sandwiched therebetween. With the surface electrodes being arranged in this manner, electricity is supplied to a wide area of the heat generation element. As a result, the heat generation element generates heat uniformly as much as possible over the wide area.
In Patent Document 1, there is disclosed a control system of an energization heating type honeycomb body. In this control system of the energization heating type honeycomb body, a resistance value of the energization heating type honeycomb body is calculated from a voltage and a current value. Then, a voltage and/or an electric current to be supplied is controlled based on the resistance value thus calculated, whereby the temperature control of the energization heating type honeycomb body is carried out.
In Patent Document 2, there is disclosed a catalytic heater energization control device which controls electric power supplied to an electrically energized heater. In this catalytic heater energization control device, the richer becomes the air fuel ratio of an air fuel mixture in an internal combustion engine, the lower the value of electric power supplied to the electrically energized heater is set.
In Patent Document 3, there is disclosed a catalyst deterioration degree detection device. In this catalyst deterioration degree detection device, an air fuel ratio at the upstream side of a catalyst is changed over from either one of a preset air fuel ratio of a lean side with respect to a stoichiometric air fuel ratio and a preset air fuel ratio of a rich side with respect to the stoichiometric air fuel ratio to the other. Then, after the change over of the air fuel ratio, an absolute amount of oxygen stored and held by the catalyst is calculated from an amount of catalyst flow-through gas which will flow through the catalyst by the time a detected value of an air fuel ratio sensor arranged at the downstream side of the catalyst reaches the above-mentioned preset air fuel ratio after the change over of the air fuel ratio, and a deviation of the above-mentioned preset air fuel ratio after the change over of the air fuel ratio with respect to the stoichiometric air fuel ratio. The degree of the deterioration of the catalyst is detected from this absolute amount.